Unable to Change Fiscal Year to align with Calendar Year

Currently our company is on a fiscal year Oct 1- Sep 30. Starting 2021 - the government requires all companies to use calendar year (Jan 1 - Dec 31) as fiscal year. How to align with new fiscal year?

If I make a new year - it still aligns with Oct 1- Sep 30. If I try to extend it to 15 months - or shorten it to 3 months Oct 1 - Dec 31 - ERPNext gives error that fiscal year must be 12 months.

I can make a new fiscal year starting Jan 1, 2021 to Dec 31, 2021 - but what will happen to transactions for period after end of currrent year (Sep 30, 2020) - and before beginning of next fiscal year (Jan 1, 2021)? Can ERPNext have transactions without a fiscal year?

Appreciate any guidance on how to resolve this business critical issue. Thanks.